This contractor will be the Coordinating Center for the collaborative clinical trial, Cardiac Arrhythmia Treatment Study (CATS). The primary objective of this trial is to see if effective drug treatment of frequent ventricular premature depolarizations in post-myocardial infarction patients will reduce the incidence of sudden cardiac death; secondary objectives are to (1) assess the impact of treatment on all-cause mortality, (2) evaluate adverse drug effects, (3) examine the clinical course of the disease in the control group, and (4) conduct selected substudies to clarify the disease process and the mechanisms of drug efficacy. A three-year recruitment period is designed, following a ten-month planning plase. Follow-up will continue two years beyond patient recruitment.